Awhile back the game was dropping boar meat & medium leather for deer I was hunting. It only happened when I did not loot the deer corpse right away. If I turned my characters field of view away from the deer I had killed, especially if I was a good distance away, the game would reward me with boar meat & leather after killing deer.

Generally the norm when breeding boar is a boar will produce offspring the same level as itself, even if it was bred to a lower level boar. The key to taming is to try and maintain close proximity and visual contact (in such a way as they cannot see you), while one is crouched and unarmed, especially when the game transitions to a new day. I have had creatures I was taming despawn while only being a few feet away from them, by turning away and losing them from my field of view, during the moment when a new day begins.

I found your post a little confusing insomuch that it read in such a way that it sounded like you were breeding boars while taming them? They cannot breed unless the taming process is complete in both animals, so if they had bred an offspring and you went back to find one of the breeding pair had transmuted to a no-star, then that occurred after the taming process.